Historically, meters measuring electrical energy, water flow, gas usage, and the like have used measurement devices, which mechanically monitor the subscriber's usage and display a reading of the usage at the meter itself. Consequently, the reading of these meters has required that human meter readers physically go to the site of the meter and manually document the readings. Clearly, this approach relies very heavily on human intervention and, thus, is very costly, time-consuming, and prone to human error. As the number of meters in a typical utility's service region has increased, in some cases into the millions, human meter reading has become prohibitive in terms of time and money.
In response, various sensing devices have been developed to automatically read utility meters and store the meter data electronically. These sensing devices, usually optical, magnetic, or photoelectric in nature, are coupled to the meter to record the meter data. Additionally, the meters have been equipped with radio frequency (RF) transceivers and control devices which enable the meters to transmit meter data over an RF link when requested to do so. Hand-held devices have been developed which include RF transceivers designed to interface with the meters' RF transceivers. These hand-held devices enable the human meter reader to simply walk by the meter's location, transmit a reading request over an RF link from the hand-held device to the meter's receiving device, wait for a response from the meter's sensing and transmitting device, and then record, manually or electronically, the meter data.
Similarly, meter reading devices have been developed for drive-by reading systems. Utility vans are equipped with RF transceivers similar to those described in the hand-held example above. The human meter reader drives by the subscriber's location, with an automated reading system in the utility van. Again, the meters are commanded to report the meter data, which is received in the van via an RF link, where the data is recorded electronically. While this methodology improves upon the previous approaches, it still requires a significant amount of human intervention and time.
Recently, there has been a concerted effort to accomplish meter reading by installing fixed communication networks that would allow data to flow from the meter all the way to the host system without human intervention. These fixed communications networks can operate using wire line or radio technology.
FIG. 1 shows a conventional fixed communication network for automated meter reading (AMR) technology. As shown in FIG. 1, a fixed communication network having wire line technology in which utility meters 10 are connected to a wide area network (WAN) 16 consisting of a suitable communications medium, including ordinary telephone lines, or the power lines that feed the meters themselves. The meters 10 are equipped with sensor and control devices 14, which are programmed to periodically read the meters and transmit the meter data to the utility's central computer 18 over the WAN 16.
One disadvantage of this approach has been that when a number of meters transmit meter data nearly simultaneously, the inherent latency on the wide area network results in packet collisions, lost data, garbled data, and general degradation of integrity across the system. To compensate for the collisions and interference between data packets destined for the central computer, due to the latency inherent in the WAN, various management schemes have been employed to ensure reliable delivery of the meter data. However, while this approach may be suitable for small systems, it does not serve the needs of a utility which monitors thousands or even millions of meters.
In an attempt to better manage the traffic in the WAN, approaches have been developed wherein meter control devices similar to those described above have been programmed to transmit meter data in response to commands received from the central computer via the WAN. By limiting the number of meter reading commands transmitted at a given time, the central computer controls the volume of data transmitted simultaneously. However, the additional WAN traffic further aggravated the degradation of data integrity due to various WAN latency effects. Thus, while these approaches may serve to eliminate the need for human meter readers, reliance on the WAN has proven these approaches to be unsatisfactory for servicing the number of meters in the typical service region.
Consequently, radio technology has tended to be the medium of choice due to its higher data rates and independence of the distribution network. The latest evolution of automated meter reading systems have made use of outbound RF communications from a fixed source (usually the utility's central station), directly to RF receivers mounted on the meters. The meters are also equipped with control devices which initiate the transfer of meter data when commanded to do so by the fixed source. The meters respond via a WAN as in the previous wire-based example. One disadvantage of these approaches is that there is still far too much interference on the WAN when all of the meters respond at about the same time. Thus, while these approaches reduce some of the WAN traffic (by eliminating outbound commands over the WAN), they are still unable to accommodate the large number of meters being polled.
It is worthy of note that the wire-based systems typically use a single frequency channel and allow the impedance and transfer characteristics of the transformers in the substation to prevent injection equipment in one station from interfering with receivers in another station. This built-in isolation in the network makes time division multiplexing less critical than for radio based metering systems. Typical fixed network radio systems also utilize a single channel to read all meters but the systems do not have a natural blocking point similar to the substation transformer utilized by distribution line carrier (DLC) networks. Also, the latency inherent in the WAN has contributed significantly to the problems associated with time division multiplexing a single frequency communications system. As a result, the systems require sophisticated management schemes to time division multiplex the channel for optimal utilization.
Changes to the network (e.g., adding a meter) or operating conditions (e.g., temperature, other WAN traffic) have exacerbated the problems associated with narrowband interference, causing information to be lost in transit to the utility's central station. Thus, a system designed to service hundreds of thousands of meters must also include the capability to keep track of changes in the network, and adapt to those changes efficiently.
Therefore, a need exists to provide a system whereby a utility company can reliably and rapidly read on the order of one million meters in the absence of any significant human intervention. Further, a need exists to provide such a system which accommodates changes to the network as well as changes in operating conditions without significant degradation of performance.